1. Technical Field of the Invention
The present invention relates to a container for maintaining an object at a specific temperature other than the ambient temperature of the environment. More specifically, this invention relates to a container which uses two materials which maintain respective different temperatures in an insulated container for establishing a temperature gradient in the container and means for maintaining an object at a constant, selected temperature between the two different temperatures during shipping or short term storage.
2. Discussion of the Prior Art
For many products, such as foods, drugs, body organs and material samples, it is desirable to maintain a specific constant temperature during transportation or storage. Refrigeration or self-heating containers provide a constant temperature for such products, but tend to be bulky, heavy and complicated to operate. In shipping, especially by air, the substantial weight of a refrigeration or self-heating container adds excessively to the costs. Additionally, refrigerated or heated containers require an external refrigeration or heating source which can be difficult to maintain and operate during shipping. Since containers for maintaining a commodity in a cooled state are by far more prevalent than containers which maintain a commodity in a heated state, the ensuing discussion focuses on refrigerated containers. However, it should be understood that the problems with the prior art and the solution offered by the invention are also applicable to containers for maintaining a commodity in a heated state.
Various insulated shipping containers which use a refrigerant have been devised for shipping. Some approaches, such as those shown in U.S. Pat. Nos. 4,294,079 and 3,971,231, have oriented a product and refrigerant within a specific insulated container in order to maintain a proper temperature.
Generally such insulated containers use ice or dry ice (solid carbon dioxide) as the refrigerant. The use of a single refrigerant in the container with the product limits the possible temperatures at which the product can be maintained. Also, temperature differences occur among products or parts of products which are closer to and farther from the refrigerant in such containers.
Therefore, a need exists for an insulated shipping container which provides a uniform, constant temperature throughout a defined volume. A need also exists for a shipping container which is lightweight, easily transportable and yet maintains an object at the appropriate user-selected constant temperature.